There were serous attempts at anti-lynching legislation in the 1920's and 1930's, and at anti-poll-tax legislation by 1940. But the first modern president to propose a broad program of *general* civil rights legislation was Truman in 1948. To show how little chance it had of passing: "A March 1948 Gallup poll revealed that 82 percent of the respondents opposed Truman's civil rights program."
https://books.google.com/books?id=A94zj6PYV7gC&pg=PT251 (He did implement some of the proposals through executive orders, however.) Even after Truman's victory in 1948, civil rights and other proposals of his faced hard going in Congress because of the filibuster in the Senate and the '"conservative coalition" of southern Democrats and Republicans. (See the cartoon at
http://history.house.gov/Exhibition...says/Keeping-the-Faith/Civil-Rights-Movement/) A lot of small-state senators from the West were opposed to any weakening of the filibuster because they saw it as the key to small-state power. (Also, they had few African American votes to worry about, and wanted southerners as allies on farm legislation.)
In short, what is surprising is not so much that it took so long to get a civil rights bill passed, but that it was possible to pass even a watered-down one in 1957.